Apoptosis is an important biological function for maintaining homeostasis in multicellular organisms. This process is genetically determined and has been shown as one of basic mechanisms conserved during evolution [M. D. Jacobsen et al., Cell, 88, pp. 347-54 (1997)].
The process of cell death in mammals involves members of the Caspase gene family, which consists of at least ten members [E. S. Alnemri et al., Cell, 87, p. 171 (1996)]. All caspases are cysteine proteases and synthesized as a precursor form. Caspases are activated by cleavage of the precursor at specific Asp residues. This generates an active heterodimer consisting of a 20 kDa and a 10 kDa subunit. This heterodimer then dimerizes with itself forming a tetramer. Activation of caspases is probably mediated by autocatalytic processes or a cascade among the caspase proteases. Once caspases are activated, they cleave a variety of target proteins causing changes in cells associated with apoptosis.
Recent work on the apoptotic process has revealed that activation of Caspase-3 is associated with DNA fragmentation [X. Liu et al., Cell, 89, pp. 175-84 (1997)]. Three factors are involved in Caspase-3 activation—Apaf-1 (apoptosis protease activating factors), cytochrome-c (which is a essential element for mitochondrial functions) and Caspase-9 [Zou et al. (1997); X. Liu et al. (1996), Cell, 86, pp. 147-57; and P. Li et al., Cell 91, pp. 479-89 (1997)].
Understanding the mechanisms of programmed cell death has important implications for preventing developmental abnormalities, as well as in the prevention of nerve cell death, smooth and cardiac muscles degeneration, and cell death associated with viral infection. Thus, there is a great need to obtain tools to study apoptosis, as well as developing inhibitors thereof.